Coded track circuit for railway train detection



July 20, 1943. H. A. THOMPSON 2,324,964

CODED TRACK CIRCUITS FOR RAILWAY TRAIN DETECTION Filed Dec. 6, 1941 mvmoR HowardAjhompyan FYQZW HIS ATTORNEY Patented July 20, 1943 CODEDTRACK CIRCUIT FOR EAILW'AY TRAIN DETECTION Howard A. Thompson, Edgewood,Pa, assignor to The Union Switch & Signal Company, Swissvale, Pa., acorporation of Pennsylvania Application December 6, 1941, Serial No.421,880

5. Claims.

My invention relates to coded track circuits for detecting the presenceof railway trains and it has special reference to the employment by suchtrack circuits of coded energy pulses that have positive and negativepolarities in alternating sequence andthat are of relatively shortindividual duration.

Generally stated, the object of my invention is to improve the designand broaden the utility of coded track. circuits of the polar impulseype just described.

A more specific object is to provide improved energy supply facilities.for polar impulse track circuits. of the single code. type. 3

Another object is to derive the polar impulse energy from non-trackbattery sources and to supplythe pulses of that energy atcodefrequencies which are much higher than those of customary direct currentcodes.

A further object is, to provide code generating facilities which are ofnew and simplified character and which incorporate self-starting andother'desirable features.

In practicing my invention I attain the above and other objects andadvantages by deriving the trackway energy from a. direct current sourceof twelve volt or other conventional control potentim; by interposing animpulse transformer between this source and the track rails; and byproviding code generating apparatus which causes this transformer toreceive from the source relatively short pulses of exciting current thatrecur several times each second and that have positive and negativepolarities in. al-

ternating sequence- I shall describe representative forms of polarimpulse coded track circuits which embody my invention and shall thenpoint out the novel features thereof in claims. These illustrativeembodiments are disclosed by the accompanying drawing in which:

Fig. l is a diagrammatic representation of a single code track circuitthat incorporates the improvements of my invention and that is of thedetection only type;

Fig. 2' shows the Trackway code for the circult of Fig. 1 and indicatesthe manner in which thatcode is produced;

. Fig. 3 illustrates a modified form of code generating'apparatus whichmay be employed at the exit end of the Fig. 1- track section; and

Fig. 4 shows. a modified form of code detectins; apparatus which may beemployed at the entrance end: of the. Fig. I track section.

In the several views of the drawing, like ref erence charactersdesignate corresponding parts. Referring first to m. 1, characters I and2- designate the conductors of a control. circuit which normally iscapable. of transmitting energy between its two ends but; which at timesis rendered incapable oisuch transmission. As shown in Fig. 1', thesecontrol circuit. conductors take the form of the two rails of asectionof railway trash. II-III which is separated from adjoiningsections the customary insulated joints 3 and through which it will beassumed that tra'flic moves in the singledirection indicated by thearrow. Suchv movement, of course, makes location II the'section entranceend. and location III the section exit end.

At this exit end 111 there is provided an impulse transformer T1 havingan output winding that is continuously connected with the section railsand an: input winding that has one center and two end terminals; asource of direct current exciting. energy for this: transformer whichhas first and second terminals B and: C and which may take the form of atwelve volt. control battery (not shown) or the like; any impedance 5which continuously connects source terminal C with the center terminalof transformer 'I'IFs' input winding; and coder relays. CTt and GT2which. repeatedly connect source terminal B first with. one and; thenwith the other of that input windingstwo end terminails andwhich'thereby cause the. transformer T1 to supply the section rails withrecurring pulsesoi outputpotential that have positive and negativepolarities. in alternating sequence.

At the section entrance end II there is provided a. track relay TR of?the code following type which has its winding connected across the railsand which holds contacts 8.--9 to the 1eit during each positive polaritypulse of winding received energy and to the right during each negativepulse of received energy; a decoding transformer DI' which. receivesprimary current under the control otthe pole changing. contact 8 of'thetrack. relay; and a code detecting. relay H. which is 01 thedirectcurrent delayed. release type and which is energized. from the decodintransformer secondary over a rectifying contact 5 or the track relay.

Two-relay coderappdratus of Fig. I

The exit end or location III apparatus just described forthe' Fig. 1track section will first be examined in greater detail. Each of thecoder relays CT! and GT2- is of'the magnetically toggled code followingtype having a delayed response of the short character later described.Looking; at device CTI, when the leitportion or its winding is energizedthe relay holds it contacts I t- L2- 3 in the left or normal position;when, however, the right portion-or the relay winding is energizedcontacts I ll2|3 then are shifted to the right or reverse position.

011cc, moreover,- eitherof these positions is established, the contactsthere remain continuously until therela winding is energized in theopposing direction. Relay GT2 performs in exactly the same manner. Whenthe left portion of its winding is energized it holdscontacts l'| 6inthe left or normal position; when, however,

the right portion of the relay winding is ener gized these contacts -16are shifted to the right or reverse position. r

In the illustrative organization shown, current for operating the firstcoder relay CT! is supplied over contact N5 of the companion relay. GT2while the current for operating that com-- panion coder device GT2 issupplied over contact [3 of the first coder relay GTl. As will be seen:

(1) relay CT2s energizing circuits cause CTZs contacts I5l6 to go totheir left or normal posi tion following eachnormal positioning of relayGTI s control contact l3 and to their right or reversed-positionfollowing each reverse positioning of thatcontrol contact; and (2)relayGTis energizing circuits cause GTls contacts I |l2.l3 to go'totheir right or reversed position following each normal positioning ofGT2s control contact l6 and to their left or normal position followingIn the complete organization of Fig. 1, each one Of those four periodsdefines the completion of a circuit through which the input winding ofimpulse transformer TT is supplied with a pulse of exciting current fromdirect current source BG. The first of these circuits extends fromsourceterminal B'throughnormal contact 55 of deviceGTZ, conductor it,normal contact ll of device GTE, conductor 19, the eft half oftransformer TTs input winding, and impedance 5 back. tosource terminalC. By it, transformer 7 interval c--d of Fig. 2.

each reversed positioning of that control con- 7' tact.

By these uniquely arranged energizing'circuits, the two coder relays GTland GT2 are caused rev peatedly to shift the positioning of theircontacts in the cyclic manner which Fig. 2 represents. In the diagram ofthat figure, the elevated portions of the CTI pattern designate a normalor left closure of contacts H'l 2i3, while the depressed portions ofthat pattern designate a reverse? or right closure of the same contacts;Similarly,.the elevated'portions of the :2

GT2 pattern designate a normal or left closure of contacts l5:-l6,while-the depressed portions of the pattern designate a reverseior rightclosure of the same contacts.

From this Fig. 2 diagram, it will be seen that: (1) if the contacts ofcoding device GT2 reach theirleft or normal position at point a, thenthe contacts of device GTI will begin movement from will begin movementfrom their reverse 'to their normal positions at the later point 1; (4).if those CTI contacts reach their normal position at point .0, then theGT2 contacts will begin movement from their reverse to theirnormalpositions at point h; and (5) if the GT2 contacts again'reach theirnormal position at point al; then theGTl contacts will start to movefrom their normalto their reverse position at the later point bl.

The just stated periods ab, 'cd, e-f, g--h and aI-bl of contactpositionfoverlap result from the earlier mentioned delayed responsecharacteristics of the two coder relay CTI and GT2. .As" long. as properpotential continues to be .appliedto the operating circuit terminalsplus'and minusv the sequence of actions diagrammed by Fig. 2 continuesto repeat itself on the .four periodbasis already indicated. The varioustime intervals in the sequence... are, of

course, dependent upon the response speeds of coder devices GT|--GT2. vi

For reasons to be madehclearrpresently, .it is preferable to arrangethat these periods a. b,

c-d, e -f and g,h of contact register recur at the rate of severaltimeseach second;

The third exciting circuit for the transformer extends from sourceterminal B through reverse contact #5 of device GT2, conductor23,.reverse contact if of device GT5, conductor 19, the'left halfoftransformer TT input winding and impedance5 back to source terminal C.By this third circuit, the transformer TT is supplied with positivepolarity exciting current during time interval cf of Fig.2.

The fourth exciting circuit for transformer TT extends from sourceterminal B through reverse contact of device GT2, conductors 23 and 28,

normal contact #2 of device GT1, conductor 24,

the right half of'the transformer input winding and impedance 5 back tosource terminal C. By that fourth circuit, the transformer is suppliedwith negative polarity exciting current during time. interval gh of Fig.2. k

Through their earlier described cyclic operations, therefore, the twocoder relays CTI and thus cause the impulse transformer TT to besuppliedwith recurring pulses of exciting current which have positiveand negative polarities in alternating sequence and which produce in thetransformer core magnetic fluxes having the general character designatedby the .TT flux D tion of Fig. 2. The alternate reversals of fluxpolarity are, of course, effected by the relatively reversed directionsof current flow through the left and right halves of the transformerinput winding.

By those recurrently reversing core fluxes there is generated in theoutput winding of transformer TT a secondary potential having thegeneral character indicated. by the Trackway code portion of Fig. 2. Asthat figure shows, this track- Way potential is alternating in polarity;it takes the form of positive and negative voltage pulses which followone another inregularly recurring sequence; each of those pulses has ahigh peak 01' impulse value; and each pair of pulses constitutes a codecycle consisting of a positive period followed by a negative period.

Preferably, these polar impulse cycles recur at a code frequency whichis much higher than that of customary direct current codes. Typicallysuch customary codes have an upper limit of the order of cycles perminute, or three cycles per second. In the polar impulse code of Figs. 1and 2, frequencies of the order of six or more cycles per second are tobe preferred and such ar readily obtainable by means of coder relaysarranged in the novel manner shown at CT!- GT2 in Fig. l. 7

Looking next at the entrance end or location II apparatus earlierdescribed for the Fig. 1 track section, it will first of all beobservedthat track relay TR also is a code following device of the magneticallytoggled or polar stick type. Such a relay is capable of transferring itscontacts from one position to the other rather rapidly and inresponse'to only a short application of winding energy. A positivepolarity pulse of the short character indicated in Fig. 2 is. thereforeefiective to shift the track relay contacts 8-9 to their normal or leftposition while a negative'polarity Pulse otcorrespondingly short.duration is efiective to shift the contactsto their right or reversedposition. I

Operation of the track relay is, therefore, exactly the same as wereeach of the positive pulses to be prolonged for the: full duration ofthe positive. codeperiod; and each of the negative pulses to beprolonged for the full duration of the "negative code period. Even withcode frequencies of the elevated. order of six. or more cycles persecond such desired operation of the track relay continues to heachieved;

As earlier indicated, the track relay TR controls a code detector relayH in such manner that the latter relay holds its contact 2.1. picked. up

when and only when the track'relay'is following 51" with those pulses,this code detector relay H receives the code frequency pulses; ofunidirectional current which hold: contact. 21 continuously picked up.In the event, however, that contacts 8-3 stay in one position.continuously, no secondary voltage is generated by transformer TT andrelay H then allowed to releaseccntact 21.

From the foregoing description. of the appas ratus at exit and entrance.locations III and II. the functioning of the complete polar impulsetrack circuit combination of Fig. 1 will have become apparent. Coderrelays CTI and GT2 operate continuously and cause exit end elements BCand TT to supply the section rails with trackway energy having the polarimpulse character represented. by the lower portion. of Fig. 2. Undervacant conditions ofthe section this energy is transmitted to entranceend track relay TR..

In responding, that relay repeatedly shifts contacts 8-9 between theirnormal and reverse positions and thereby causes code detecting relay Hto hold contact 21- continucusly. picked up. This picked up conditionpeisists, quite. obviously, as long as track section IIII-I remainsvacant. Entry of a train into the section by-passcs rails .l- 2 in theusual manner and thereby cuts 03ft all energy reception; by relay TR.Such cut-0E causes contacts 39to remain continuously in the position towhichthey. were last energized ay'IR serves to pole change the itisresponsive to each pulse ofoutput voltage and thereby deenergizes codedetecting relay H. As a result of that deenergization, contact 21 nowreleases.

'As .the train passes out of section IIIII, transmission. of: the-polar' impulse energy through entrance end trackrelay TB is once moreresumed; contacts 8-4! thereof again iollow code, transformer. DT oncemore supplies energizing current to the winding of relay I-l, andcontact[8 of that relay again picks Any suitable use of the code detectorrclays contact 21. may,.of course, be made and because of the diversityof such possible uses there has been no attemptto represent anyparticular one of them; Typically, however, they will be of thedetection. only'variety wherein relay H performs the single function ofdistinguishing between vacant and occupied conditions of the associatedtrack section. Such a function is, of course, required in many signalingsystem applications of commercially well-known character..

,Single relay coder apparatus of Fig. 3

Referring to Fig. 3, I have there shown an alternative arrangement forgenerating polar impulse code of the general character indi-- cated byFig; 2. In this arrangement only one polarized code following relay isused the exit location III and it is shown in the form of a device GT3.

In these modified exit end facilities of Fig. 3, use is made of animpulse transformer TTl which corresponds to device T1 of Fig. l butwhich differs therefrom in being equipped with a. second output winding.39 by which operating energy is. supplied to relay GT3. That relay isprovided with a single contact 32 over which direct current sourceB-Csupplies exciting current to the input Winding of transformer TTI.

when contact 32 occupies left hernia? position shown, the flow ofexciting current is upwardly through the lower half of the trans--former and the efiect of. a negative or: citing pulse (see the Flux ofFig. 2) is had; Whcmhowcver, contact 3.. in the right or reverseposition, the fl0WOf.QXCll;ll1Z current isdownwardly through the upperhalf of he transformer primary and the eifect or" a no u to pulse ofexciting-current (again see Fig. 2) then is'had.

Interposed between output winding of; transformer T1! and the trackrails is a current limiting impedance 33 which performs the samefunctionas does elementfi of the Fig. 1 combination, but which permits theeneration or substantially fullv transformer even during shunted.conditions of the suppne track. rails l.-2..

Thesingle coder relay GT3 of Fig. 3 has response characteristics whichare generally similar to those earlier described for I C'I'i--CH2 ofFig, It. That is, flow of one: ing current through the relay winding inthe direction of from left to right causes contact 32 to go to the leftor normal position; likewise, flow of relay winding current in theopposite or right toleft direction causes contact 32 to go to the rightorreverse position. Like coder relay devices CTICT2, moreover, thisrelay (3T3 is of the delayed responding type.

In the code generating combination of Fig.

Prop

that results from; each establishment of an exciting. connection. In theparticular organization illustrated, relay GT3 thus is caused to'shiftcontact 32 to the opposing position a short time 'following each suchestablishment.

Looking more closely at Fig. 3, assume that contact 32 has just moved tothe illustrated normal position wherein negative polarity current issupplied to the primary of transformer 'ITl and positive polaritypotential is asa result ofsuch application being generated in'each ofthe transformerstwo output windings. Such generation in winding 35}.fio'ws' current from the right to the left through relay GT3 and thuscauses contransfer contact 32. between thenormal and the reversepositions. 7

By such transfer, tr'ansformerTTl iscaused to impress upon rails l-Zcoded trackway energy of the polar impulse characterrepresented in Fig.2. By choosing the responsecharacteristics of relay GT3 the frequency ofsuch code pulse application may, quite obviously, be selected withinwide limits. I Preferably, however, a frequency of'the order of six ormore cycles; per second is to be desired. 1 Single-relay detector appamfus oj Fig, 4 Entrance end code detecting facilities of the characterrepresented at location II'in Fig. 1 are usable with code generatingapparatus not only of the two relay type shown at Fig.'1s location 111but also of the single relaytype which Fig. 3

illustrates.

Such facilities utilize, as had been seen, a code following track relayTB of conventional polar stick character plus a code detecting relay Hand an energizing transformer DT therefor. "i 1 In Fig. 4, I haverepresented a simplified form of code detecting equipment wherein only asingle relay TR! is utilized. This relay isa non-code following trackdevice which'receives energy from the rails through a relaytransform'erRT and a full wave rectifier 35. It has a contact 2Twhich performs thesame function as does the similarly designated element of Fig. 1, andwhich has slow releasing characteristics. f Reception at Fig. 4slocation II of polar impulse trackway energy, such as the codegenerating apparatus of either Fig. 1 or 3 produces, causes transformerRT and rectifier 35 to impress upon relay TRI pulses of unidirectionalenergizing current which recur at code pulse frequency and which areeffective to hold contact 21 continuously picked up. Entry of a traininto the section of which Fig. 4s location 11 marks the entrance cutsoff all of these energy pulses and thereby allows contact 2! to release.As the train passes out of the section, transmission of the coded polarimpulse energy through transformer RT is once more resumed and relay TRis caused again to pick up contact 21. p f

This Fig. 4 arrangement is best suited for use with code frequencies ofcomparatively, high character, such as the six or more cycles per secondearlier: named. With such frequencies therelease period for relay 'I'Rlscontact Zlmay be reduced sufficiently to provide a very quick shuntingresponse. a

Summary The polar impulse coded track circuits herein shown arealternative to a detector only organization which is disclosed andclaimed by my copending application Serial No. 412,624 filed onSeptember 27, 1941, forfCoded track circuits for railway trafiiccontrol. For the track circuits of the present application, therefore,the same, broad advantages may be claimed as are enumerated by mycopending application just identified.

These broad advantages flow from the use of the polar impulse principleand include a lowering of power requirements, a raising of immunity tofalse operation by foreign currents, an elimination of operatingdifficulties due to storage energy persistence, a lowering of codedistortion effect, and an improvement in shunting sensitivity.

In addition, the novel code generating apparatus of this applictionbroadens the utility of coded track circuits of the -polar impulse typeby: (1) improving the design of energy supply facilities for "singlecode track circuits; (2) deriving the polar impulse energy from nontrackbattery sources and supplying the pulses of that energy at. codefrequencies which are much higher than those of customary direct currentcodes and which approximate the characteristics of an alternatingcurrent track circuit;

and (3) permitting allof the code generating devices to be of similardesign.

In each of the organizations moreover, the code generating apparatus isinherently self-starting and automatically begins to function whenenergy of a proper character is impressed upon the terminals ofits'driving circuits. I .1

From the foregoing it will accordingly 'be seen that the improved polarimpulse coded track circuits of my invention are of broad utility andthat their application is by no means restricted to the detector onlyforms which are herein shown by way of illustration.

Although I have herein shown and described only representative forms ofcoded track cirmy invention, what I 1. In track circuit energy supplymeans, in

, combination, a transformer having an output gizedin one direction andwhich occupy a reversed position when and after the relay is energizedin the opposing direction, an energizing circiut for said second relaywhich'is controlled by a contact of said first relay and which causesthe second relay contacts to go to their normal of Figs. 1 and 3,

position following each normal positioning of the first relay contactsand to their reversed -posi-- tion following each reversed positioningof the first relay contacts, an energizing circuit for said first relaywhich is controlled by a contact of said second relay and which causesthe first re lay contacts to go to their reversed position followingeach normal positioning of the second rel-- lay contacts and to theirnormal position following each reversed positioning of the second relaycontacts, and circuits including contacts of said first and secondrelays over which said first terminal of said direct current energysource is repeatedly connected first with one and then with the other ofsaid two end terminals of said transformer input winding and by whichsaid transformer output winding is caused to supply recurring pulses ofoutput potential that have positive and negative polarities inalternating sequence.

2. In combination, a pair of conductors, a transformer connected inenergy supplying relation with said conductors, a source of directcurrent exciting energy for said transformer, first and second coderrelays each having contacts which occupy a normal position when andafter the relay is energized in one direction and which occupy areversed position when and after the relay is energized in the opposingdirection, an

energizing circuit for said second relay which is controlled by acontact of said first relay and which causes the secondrelay contacts togo to their normal position following each normal positioning of thefirst relay contacts and to their reversed position following eachreversed posiposition following each normal positioning of the secondrelay contacts and to their normal position following each reversedpositioning of the second relay contacts, and circuits includingcontacts of said first and second coder relays over which saidtransformer primary is from said source supplied with exciting currentof a character that causes the transformer to supply said conductorswith recurring pulses of positive polarity energy which are separated byintervening pulses of negative polarity energy.

3. In combination, current-receiving apparatus, a source of energytherefor, first and second coder relays each having contacts whichoccupy a normal position when and after the relay is energized in onedirection and which occupy a reversed position when and after the relayis energized in the opposing direction, an energizing circuit for saidsecond relay which is controlled by a contact of said first relay andwhich causes the second relay contacts to go to their normal positionfollowing each normal positioning of the first relay contacts and totheir reversed position following each reversed positioning of the firstrelay contacts, an energizing circuit for said first relay which iscontrolled by a contact of said second relay and which causes the firstrelay contacts to go to their reversed position following each normalpositioning of the second relay contacts and to their normal positionfollowing each reversed positioning of the second relay contacts, andcircuits governed by contacts of said first and second coder relays overwhich said apparatus is from said source supplied with recurring pulsesof positive polarity energy that are separated by intervening pulses ofnegative polarity energy.

4. In combination, current-receiving I apparatus, a source of energytherefor, first and second coder relays each having contacts whichoccupy a normal position when and after the relay is energized in onedirection and which occupy a reversed position when and after the relayi energized in the opposing direction, an energizing circuit for saidsecond relay which is controlled by a contact of said first relay andwhich causes the second relay contacts to go to their normal positionfollowing each normal positioning of the first relay contacts and totheir reversed position following each reversed positioning of the firstrelay contacts, an energizing circuit for said first relay which iscontrolled by a contact of said second relay and which causes the firstrelay contacts to go to their reversedposition following each normalpositioning of the second relay contacts and to their normal positionfollowing each reversed positioning of the second relay contacts, afirst circuit which connects said source in positive energy supplyingrelation with said apparatus when the contacts of both of said relaysare in their normal position, a second circuit which connects saidsource in negative energy supplying relation with said apparatus whenthe contacts of said second'relay are in their normal position and thecontacts of said first relay are in their reversed position, a thirdcircuit which connects said source in positive energy supplying relationwith said apparatus when the contacts of both of said relays are intheir reversed position, and a fourth circuit which connects said sourcein negative energy supplying relation with said apparatus when thecontacts of said second relay are in their reversed position and thecontacts of said first relay ar in their normal position.

5. In combination, current-receiving apparatus, a source of energytherefor, first and second coder relays each having contacts whichoccupy a normal position when and after the relay is energized in onedirection and which occupy a reversed position when and after the relayis energized in the opposing direction, an energizing circuit for saidsecond relay which is controlled by a contact of said first relay andwhich causes the second relay contacts to go to their normal positionfollowing each normal positioning of the first relay contacts and totheir reversed position following each reversed positioning of the firstrelay contacts, an energizing circuit for said first, relay which iscontrolled by a contact of said second relay and which causes the firstrelay contacts to go to their reversed position following each normalpositioning of the second relay contacts and to their normal positionfollowing each reversed positioning of the second relay contacts, afirst circuit completed over a normal contact of said second relay and anormal contact of said first relay for connecting said source inpositive energy supplying relation with said apparatus, a second circuitcompleted over a normal contact of said second relay and a reversedcontact of said first relay for connecting said source in negativeenergy supplying re lation with said apparatus, a third circuitcompleted over a reversed contact of said second relay and a reversedcontact of said first relay for connecting said source in positiveenergy supplying relation with said apparatus, and a fourth circuitcompleted over a reversed contact of said second relay and a normalcontact of said first relay for connecting said source in negative energy supplying relation with said apparatus.

HOWARD A. THOMPSON.

